This invention relates generally to photolithographic processes for manufacturing semiconductors.
In photolithographic processes, a radiation pattern from a mask is transferred to a photoresist. The exposed portions of the photoresist are either made more or less soluble. The more soluble material is then removed to transfer the pattern from a mask to the pattern of photoresist on a substrate. The photoresist pattern may then be utilized as an etch mask to etch a corresponding pattern into the semiconductor substrate.
It is known that a polymer and, more particularly, an acid catalyzed cross-linking material may be utilized to form an etch resistant cap or shell over a photoresist line. The material may be a resolution enhancement lithography assisted by chemical shrink (RELACS) polymer. In the RELACS process, a photolithographically defined resist pattern may be enhanced or thickened using a RELACS overcoating. The RELACS overcoating grows isotropically. That is, it grows equally on the top and sides of the photoresist line. This horizontal growth, in effect, increases the size of the resulting transferred pattern, allowing feature sizes to be adjusted after patterning the rest (such as reducing the size of a hole, patterning in a photoresist, when the patterning process is not sensitive enough to produce holes as small as the desired size).
On the other hand, the RELACS overcoating may be useful in improving the quality of the overall resist line. For example, some resists may be tailored to make it easy to define their shape, but they may be poor at transferring that shape to a substrate. The cap or shell provided by the RELACS process may add this latter property of enabling the transfer of the pattern to the substrate. Because the RELACS shell or cap is self-aligned with the underlying resist, relatively thin resist patterns can be augmented.
Another application for RELACS is where a resist pattern may be poorly resolved. For example, a straight line portion of resist may be subject to having breaks through it. A conformal coating, such as RELACS, may fill in these gaps and make the pattern more accurate.
Finally, current lithography may use smaller resist thicknesses. There are several reasons for this. One reason is that the ability to pattern thin resists may be better. In 193 or 157 nanometer photolithography, less robust photoresists may be utilized that do not stand up well to ensuing plasma etching. In extreme ultraviolet lithography, very thin films must be used because of the problem of absorption of the extreme ultraviolet radiation or due to the collapse behavior of the resist features. In order to render the features more resistant to the pattern transfer process (i.e. to confer greater etch resistance to them), a conformal coating, such as RELACS, may serve to improve the overall etch resistance of the features. As the size of the resist features decrease with each succeeding generation of manufacture, the roughness of the features forming the photoresist pattern becomes more important to control as it become a larger percentage of the total size of the feature. This phenomenon gives rise to so-called line edge or line width roughness. Thus, a conformal coating, such as RELACS, may improve the overall roughness of the features.
For all of these reasons, the RELACS process may be highly desirable. However, it would be equally desirable to have a RELACS type process that does not unnecessarily widen the capped photoresist features.
Thus, there is a need for better ways to anisotropically cap photoresist features in semiconductor manufacturing processes.